As a method of improving a motion-picture response by performing a pseudo impulse display of a liquid crystal display device (hereinafter referred to as an “LCD”) performing a hold type display black insertion techniques, such as, black frame insertion, and backlight blinking are being widely used in commercially available LCDs.
However, these techniques involve the problem that the luminance is lowered in response to the raise of the black insertion rate for raising the effect of improvement of the motion-picture response.
Then, as a pseudo impulse display method for improving motion-picture response avoiding the lowering of the luminance (hereinafter referred to as the “improved pseudo impulse drive”), the following techniques have been proposed.
1. Driving a display panel by a high frame rate (for example, 120 Hz) two or more times an ordinary display frame rate (for example, 60 Hz).
2. Carrying out a frame rate conversion from one frame having an ordinary frame rate to a plurality of sub frames having a high frame rate (for example, two sub frames in a case of 60 Hz→120 Hz), and converting the gradations.
Note that, the method of the frame rate conversion may be either a method of production of an interpolation frame or a method of merely copying original frame.
3. Since the gradation conversion is carried out so that the luminance of the frame of a certain pixel before gradation conversion and a mean luminance of a plurality of sub frames after frame rate conversion become the same, a drop in the luminance does not occur.
FIG. 1 is a block diagram showing an example of the configuration of an LCD use image processing apparatus adopting the improved pseudo impulse drive method.
This image processing apparatus 1 has a frame rate conversion portion 2, a gradation conversion portion 3, and a liquid crystal panel 4. The gradation conversion portion 3 includes a first sub frame use first conversion portion 31, a second sub frame use second conversion portion 32, and a sub frame selecting and outputting portion 33.
Here, the improved pseudo impulse drive processing in the image processing apparatus 1 in FIG. 1 will be explained with reference to FIG. 2 to FIG. 5.
FIG. 2 is a diagram showing an output gradation characteristic of a frame before frame rate conversion and gradation conversion by a general hold drive, FIG. 3 is a diagram showing a gradation conversion characteristic, FIG. 4 is a diagram showing an output gradation characteristic of a sub frame after frame rate conversion and gradation conversion in a case where the improved pseudo impulse drive is employed, and FIG. 5 is a diagram showing a transmittance characteristic of the sub frame after frame rate conversion and gradation conversion in the case where the improved pseudo impulse drive is employed.
The results by converting each frame of 60 Hz to a first sub frame and a second sub frame of 120 Hz as shown in FIG. 2, then further converting the gradation of the first and second sub frames according to the characteristics shown by the solid lines A and A′ in FIG. 3, are shown in FIG. 4.
Since the response of a liquid crystal at this time becomes a pseudo impulse resembling the impulse waveform as shown in FIG. 5, therefore the liquid crystal motion-picture response due to the hold type display is improved.